Alright, I'm finally getting around to writing some stuff about it! Blink asked me to explain how I have been going about things with the semi-invisible section of Survival, so I'm going to try to put things in writing as best as I can.
Playing TF's semi-invisible is a lot different than playing a "conventional" TGM invisible challenge. Whereas TGM's invisible credit rolls are a mere minute of intense challenge separating you from success, TF's semi-invisible is about dragging out a comparatively easy game out for as long as possible. Rather than subject the player to high gravity, it asymtotically approaches full invisibility by reducing the frequency of visibility flashes.
Every four lines you clear, the number of pieces it takes to trigger a reveal of playfield state increases by one. In fact, it takes only one piece to trigger a reveal at the start. The obvious early strategy is to play relatively quickly to keep the field mostly visible as you get ready for playing actual stretches of invisibility.
When the field starts being invisible more often, you'll obviously want to be able to remember where everything is. It is difficult to explain how to work on improving the skill of visualizing the stack, but here are a few tips: +Focus primarily on remembering the outline of the top of the stack. Trying to remember every last detail is too taxing, and remembering the top will give you a really good idea of what is going on. It also won't usually change when you clear lines unless you clear all the way down to garbage below.
+Keep the top relatively flat so it is easier to remember accurately. Stacking unevenly or setting up slides and twists are not usually recommended. Obviously, this means that t-spinning is not generally a good idea.
If we were talking about TGM invisible, I'd say that the best thing to do if you forget part of the stack would be to stack flat over it. However, the goal in TGM invisible credit rolls is to last 60 seconds while making as many lines as possible. In Survival however, your priority is, well... survival. With a bag randomizer, hold, low gravity, and ghost, you have plenty of tools to turtle and BS your way through.
One little trick you can use is to measure the elevation of a column using the ghost piece. However, be careful about how you interpret this information. The ghost piece might be suspended on something, and you might get the impression that the topmost solid in a column is higher than it really is. The I-piece is very useful for doing this sort of "tracing" since it can't hang from anything in its vertical orientation.
It helps to do occasional rotation or shift checks to confirm your visualisation of the stack. Sometimes using the ghost piece won't give you the full picture or there won't be enough time to check things out before the piece touches down. If you think a piece should be stuck after you drop it into place, soft drop it in and try shifting it around. If it fails on both shift directions, you had the right idea. If it wiggles around, you might want to reconsider your image of the stack.
Wallkick checks are also useful for validating your understanding of the stack without expending many lock delay resets.
It can also be useful to use the active piece to understand the field and then Hold swap out for something you actually want to place. (That's right KevinDDR -- I'm advocating the use of Kevin Holds for Survival.) If you have an I-piece active, you can get a quick sketch of half of the stack by sending it to the wall in the vertical orientation, maybe do a few quick physical checks, then swap the piece out for whatever you've got in Hold to make an actual placement.
I think that's a pretty good look at all the silly stuff you can use to turtle and BS in Survival. Feel free to post if you have any other questions or know of something I haven't covered in this post.
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